The present invention relates to electron guns for emitting beams of electrons and, more particularly, to a novel electron gun emitting a blankable electron beam which appears, at a target external to the electron gun, to remain stationary on the electron gun axis and vary only in intensity and not in position.
Electron beam-emitting means are useful for a large class of apparatus, including electron-beam-addressable memories of the type discussed and claimed in U.S. Pat. No. 3,534,219, issued Oct. 13, 1970, assigned to the assignee of the present invention and incorporated herein by reference. In such electron-beam-addressable memories, the electron beam is deflected to pass through one of a multiplicity of arrayed apertures in a lens electrode and with the electron beam current density being modulatable to values thereof between essentially zero current density and the full current density available from the electron gun. During modulation, the electron beam emitted from the electron gun often exhibits spatial movement, as well as intensity change, with these spatial movements causing the electron beam to impinge upon other lens apertures and address memory target sites other than the target site which it is desired to access at that particular instant. It is therefore desirable to provide an electron gun which is not only capable of being modulated, to change the current intensity of the beam emitted therefrom, but which is also capable of providing an electron beam lying substantially along the central axis of the electron gun for all values of beam current intensity, and without spatial motion of the beam at the target.